When viewing table data in the Schema Browser, multiple search criteria are used in the 'Filter or Sort the table data' window. In order to keep them intact, the search criteria is commented out by suffixing it with "--". However, when all the search criteria is commented out, an "Ora-00936: missing expression" error is given.
Toad is seeing some text in the filter and sticking a "WHERE" before it.
It looked like this:
ROWID, empno, ename, job,
mgr, hiredate, sal,
-- ename like '%S%'
-- job like '%S%'
Make the first criteria of the filter "1=1" and do not comment it. That way there will be some criteria to run after the WHERE clause, but it will not affect the query.